February 2013 Archives

More Wireless Ideas for Ham Radio

2.400 GHz + 900 MHz = 3.300GHz
2.483 GHz + 900 MHz = 3.383GHz

900MHz can be derived from one of the VCOs in a 900MHz Motorola Maxtrac (the RX VCO is most appropriate, as it is not modulated), mixed with 2.4GHz from a WiFi card (using circulators if necessary so T/R PIN diode switches aren't necessary, nor the detection circuitry), and filtered using stripline, stubs, and pipe-cap (cavity) filters. Gain may be provided by MMICs, and power modules as well. No need to use fancy boards until you get into the receive side of things or to prevent the PA from ringing.

The result is that one can -- today -- build a 100Mbit/s link using a pair of 802.11n cards on 2.4GHz. And 3.3GHz - 3.4GHz is only half the band; there's another half to go (but the weak-signal guys will complain if you cover them up on 3.456 GHz) of the 200MHz band. One would have to source certain components from eBay, which means the supply of those parts is limited as they are often from surplus.

But what would one do with 100Mbit/s data between two places on the ham band? That's a great question. To date, my only thought has been digitizing RF on one side of the world and spitting it across the datalink to the other side. This is useful for remote repeater receivers, as one needs to determine the time between point A, point B, coding, repeating, buffering, etc. before comparing the two signals for quality and selecting one. But 802.11n is half-duplex by nature.

Windload Study of the AT&T Horn


This PDF contains a study performed by Colorado State University commissioned by Rose Engineering and AT&T to determine the loading effects of multiple horns mounted on a tower. Amazingly, it was discovered that at certain angles, the horns cause a wake which shields the horn behind it from the wind. A lot of boring tables, but check out the pictures.

Of note in this document:

* Windload numbers for 1, 2, and 4 horns at 100MPH
* Dimensions of both the pyramidal (KS-15676) Friis/Beck/Hogg Horn and the Gabriel horn (local copy) on Pages 91 and 93.



Voluntary Coordination in Ham Radio

I just read about the 3.65 GHz band that the FCC has released to be populated. The short version is this: You register with the FCC using ULS, pay the commercial fee ($260), then you register your station when you get your license. The license term is ten years. The band is only 50MHz, and you have to protect (not operate near or shield) the existing FSS ground stations:

http://licensing.fcc.gov/prod/ib/forms/help/GrandFatherList.pdf

My information came from here:

http://www.tranzeo.com/allowed/Tranzeo_3.65GHz_License_USA_Whitepaper.pdf

However, equipment is made that covers 3.3GHz to 3.8GHz. 3.3-3.5GHz is an Amateur Radio Service band under Part 97.

This got me to thinking that it may be possible in the future for hams to voluntarily coordinate activities with each other and the FCC by putting data into a public database. However, that data would have to be periodically verified and/or vouched for. This certainly could ease coordinating various operations throughout the ham bands, as one certainly wouldn't want to interfere with another mode unwittingly. However, there is a fixed amount of spectrum, so that has to be weighed as well. Voluntary coordination makes the most sense when it comes to repeaters and data links, as the bandwidth of data links makes them somewhat difficult to locate (finding a 100KHz wide carrier with a 7KHz (5KHz) wide FM radio is not terribly useful unless the radio has a signal strength meter.

It's certainly a nice thought.

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